package com.jh.fcsm.common.redis;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.dao.DataAccessException;
import org.springframework.data.redis.connection.RedisConnection;
import org.springframework.data.redis.core.RedisCallback;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.serializer.StringRedisSerializer;

/**
 * Redis distributed lock implementation.
 *
 * @author szx
 * @date:2018年4月18日
 */
@SuppressWarnings({"rawtypes", "unchecked"})
public class RedisDistributedLock {

    private static final Logger logger = LoggerFactory.getLogger(RedisDistributedLock.class);
    private static final int DEFAULT_ACQUIRY_RESOLUTION_MILLIS = 100;
    private final RedisTemplate redisTemplate;
    private final String lockKey;
    /**
     * 锁超时时间，防止线程入锁后，无限执行等待
     */
    private int expireMsecs = 60 * 1000;
    /**
     * 锁等待时间，防止线程饥饿
     */
    private int timeoutMsecs = 10 * 1000;

    /**
     * Detailed constructor with default acquire timeout 10000 msecs and lock
     * expiration of 60000 msecs.
     *
     * @param lockKey lock key (ex. account:1, ...)
     */
    public RedisDistributedLock(RedisTemplate redisTemplate, String lockKey) {
        this.redisTemplate = redisTemplate;
        this.lockKey = "LOCK_" + lockKey;
    }

    /**
     * Detailed constructor with default lock expiration of 60000 msecs.
     */
    public RedisDistributedLock(RedisTemplate redisTemplate, String lockKey, int timeoutMsecs) {
        this(redisTemplate, lockKey);
        this.timeoutMsecs = timeoutMsecs;
    }

    /**
     * Detailed constructor.
     */
    public RedisDistributedLock(RedisTemplate redisTemplate, String lockKey, int timeoutMsecs, int expireMsecs) {
        this(redisTemplate, lockKey, timeoutMsecs);
        this.expireMsecs = expireMsecs;
    }

    /**
     * @return lock key
     */
    public String getLockKey() {
        return lockKey;
    }

    private String get(final String key) {
        Object obj = null;
        try {
            obj = redisTemplate.execute(new RedisCallback<Object>() {

                @Override
                public Object doInRedis(RedisConnection connection) throws DataAccessException {
                    StringRedisSerializer serializer = new StringRedisSerializer();
                    byte[] data = connection.get(serializer.serialize(key));
                    connection.close();
//					if (data == null) {
//						return null;
//					}
                    return serializer.deserialize(data);
                }
            });
        } catch (Exception e) {
            logger.error("get redis error, key : ", key);
        }
        return obj != null ? obj.toString() : null;
    }

    private boolean setNX(final String key, final String value) {
        Object obj = null;
        try {
            obj = redisTemplate.execute(new RedisCallback<Object>() {

                @Override
                public Object doInRedis(RedisConnection connection) throws DataAccessException {
                    StringRedisSerializer serializer = new StringRedisSerializer();
                    Boolean success = connection.setNX(serializer.serialize(key), serializer.serialize(value));
                    connection.close();
                    return success;
                }
            });
        } catch (Exception e) {
            logger.error("setNX redis error, key : ", key);
        }
        return obj != null ? (Boolean) obj : false;
    }

    private String getSet(final String key, final String value) {
        Object obj = null;
        try {
            obj = redisTemplate.execute(new RedisCallback<Object>() {

                @Override
                public Object doInRedis(RedisConnection connection) throws DataAccessException {
                    StringRedisSerializer serializer = new StringRedisSerializer();
                    Object obj = connection.getSet(serializer.serialize(key), serializer.serialize(value));
                    connection.close();
                    return obj;
                }
            });
        } catch (Exception e) {
            logger.error("getSet redis error, key : ", key);
        }
        return obj != null ? obj.toString() : null;
    }

    /**
     * 获得 lock. 实现思路: 主要是使用了redis 的setnx命令,缓存了锁. reids缓存的key是锁的key,所有的共享,
     * value是锁的到期时间(注意:这里把过期时间放在value了,没有时间上设置其超时时间) 执行过程:
     * 1.通过setnx尝试设置某个key的值,成功(当前没有这个锁)则返回,成功获得锁
     * 2.锁已经存在则获取锁的到期时间,和当前时间比较,超时的话,则设置新的值
     *
     * @return true if lock is acquired, false acquire timeouted
     * @throws InterruptedException in case of thread interruption
     */
    public boolean lock() throws InterruptedException {
        int timeout = timeoutMsecs;
        while (timeout >= 0) {
            long expires = System.currentTimeMillis() + expireMsecs + 1;
            // 锁到期时间
            String expiresStr = String.valueOf(expires);
            if (this.setNX(lockKey, expiresStr)) {
                logger.info("lock by setNx key : " + lockKey);
                // lock acquired
                return true;
            }
            String currentValueStr = this.get(lockKey);
            // 判断是否为空，不为空的情况下，如果被其他线程设置了值，则第二个条件判断是过期的
            if (currentValueStr != null && Long.parseLong(currentValueStr) < System.currentTimeMillis()) {
                // 获取上一个锁到期时间，并设置现在锁的到期时间
                // 只有一个线程才能获取上一个线上的设置时间，因为jedis.getSet是同步的
                logger.info("lock is timeout set new expire, key : ", lockKey);
                String oldValueStr = this.getSet(lockKey, expiresStr);
                // 防止误删（覆盖，因为key是相同的）了他人的锁——这里达不到效果，这里值会被覆盖，但是因为什么相差了很少的时间，所以可以接受
                if (oldValueStr != null && oldValueStr.equals(currentValueStr)) {
                    // [分布式的情况下]:如过这个时候，多个线程恰好都到了这里，但是只有一个线程的设置值和当前值相同，他才有权利获取锁
                    logger.info("current thread acquired lock key : ", lockKey);
                    return true;
                }
            }
            // 重试
            timeout -= DEFAULT_ACQUIRY_RESOLUTION_MILLIS;
            /*
             * 延迟100 毫秒, 这里使用随机时间可能会好一点,可以防止饥饿进程的出现,即,当同时到达多个进程,
             * 只会有一个进程获得锁,其他的都用同样的频率进行尝试,后面有来了一些进行,也以同样的频率申请锁,这将可能导致前面来的锁得不到满足.
             * 使用随机的等待时间可以一定程度上保证公平性
             */
            Thread.sleep(DEFAULT_ACQUIRY_RESOLUTION_MILLIS);
        }
        return false;
    }

    public void unlock() {
        redisTemplate.delete(lockKey);
    }
}
